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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Posted on 26 April 2012 by John Mason

The fact that carbon dioxide is a 'greenhouse gas' - a gas that prevents a certain amount of heat radiation escaping back to space and thus maintains a generally warm climate on Earth, goes back to an idea that was first conceived, though not specifically with respect to CO2, nearly 200 years ago. The three-part tale of how this important physical property, its role in the geological past and understanding how it may affect our future, covers about two centuries of enquiry, discovery, innovation and problem-solving.

To pick up the scientific trail of what is today known as the Greenhouse Effect, we need to travel back in time to France in the 1820s. Napoleon, defeated at the Battle of Waterloo just a few years previously, had just died, but somebody who had at one time undertaken significant engineering and academic projects for the late Emperor was now busily engaged on his investigations of the physical world, with a specific interest in the behaviour of heat. This was Jean Baptiste Joseph Fourier (1768–1830).

Fourier had calculated that a planetary object the size of Earth should, quite simply, not be as warm as it is at its distance from the Sun. Therefore, he reasoned, there must be something else apart from incoming solar radiation, some other factor that keeps the planet warmer. One suggestion he came up with was that the energy coming in from the sun in the form of visible and ultra-violet light (known back then as "luminous heat") was easily able to pass through Earth's atmosphere and heat up the planet's surface, but that the "non-luminous heat" (now known as infra-red radiation) then emitted by the Earth's surface could not make it back in the opposite direction quite so readily. The warmed air must, he reasoned, act as some kind of insulating blanket. That was about as far as he got with the idea back then, as the detailed measurements required to explore this hypothesis were not available, given the technology of the day.

above: the Grandfathers of Climate Science

Some 40 years later, the thread was picked up again. To Victorian natural historian and pioneer in Alpine climbing, John Tyndall (1820-1893), the evidence, controversial at the time but now mainstream, clearly indicated that at one time much of northern Europe had been covered by ice-caps. However, what was far from clear was how the climate could change in such a drastic manner. Among the possibilities Tyndall considered was variations in the composition of the atmosphere, and via a series of experiments he made the discovery that water-vapour was an important heat-trapping agent. He also found that carbon dioxide was very good at trapping heat, despite being a trace gas occurring in the hundreds of parts per million (ppm) range. Hundreds of parts per million may not sound like a lot, but some compounds have important properties at such concentrations: for example, 500ppm of hydrogen sulphide in air may lead to asphyxia, as any health and safety fact-sheet on the gas will tell you.

Tyndall's interesting discovery did not completely solve the ice-ages riddle: that came much later. But it planted the seed of an idea that was revisited towards the end of the 19th Century by Swedish scientist Svante Arrhenius (1859-1927). Reasoning that, because it fluctuated daily, water vapour was continually recycling itself in and out of the atmosphere, he turned his attention to carbon dioxide, a gas resident for a long time in the atmosphere whose concentration was only (at that time) dramatically changed by major sources such as volcanoes or major drawdowns such as unusual and massive episodes of mineral weathering or the evolution of photosynthetic plants: events that occur on very long, geological timescales. Arrhenius figured out that an increase in the amount of carbon dioxide in the atmosphere would result in a certain amount of warming. In addition, it was already known via the Clausius-Clapeyron relation, that warmer air can hold more water vapour: the amount is about 7% more per degree Celsius of warming. And that additional water vapour would in turn cause further warming - this being a positive feedback, in which carbon dioxide acts as a direct regulator of temperature, and is then joined in that role by more water vapour as temperatures increase.

Through further work Arrhenius determined that if you halved the amount of atmospheric carbon dioxide, the temperature of Europe could drop by as much as 4-5°C. But could such a change, big enough to cause an ice-age, occur? He turned to colleague Arvid Hogbom (1857-1940), who had been investigating natural carbon dioxide cycles, to see if it could. Hogbom had, at the time, started to consider carbon dioxide emissions from factories (simple enough if you know, for example, how many tons of coal each factory burns a year). He had been surprised to find that man-made emission rates were very similar to those occurring in nature. Back in the 1890s, that of course represented a tiny fraction of the fossil fuels that we burn today; but what, they asked themselves, might happen if mankind burnt ever-increasing amounts over many centuries? Side-tracking from the ice-age research, Arrhenius ran calculations to see what a doubling of carbon dioxide levels might do to temperatures. He came up with an answer of 5-6°C of warming as a globally-averaged figure.

Back then, at 1890s burning-rates, they didn't see this as a problem: firstly at those rates it would take thousands of years for the doubling to take place and secondly the oceans were thought to be able to absorb five-sixths of the emissions. By the time the hypothesis appeared in a popular book that was published in 1908, the burning-rate had already gone up significantly, so in accordance with that change they revised the doubling-time down to a few centuries, but it was still something of a scientific curiosity, the stuff of after-dinner conversations.

The findings did meet with a lot of skepticism during the early 20th Century: the objections were centered around claims of oversimplification, failure to factor in changes in cloudiness, and results of laboratory tests by another Swede, Knut Ångström (1857-1910). Ångström instructed a laboratory assistant to measure the passage of infra-red radiation through a tube filled with carbon dioxide. The tests began with slightly lower amounts of the gas than would be found in a complete section of the atmosphere from top to bottom - although to truly represent the atmosphere, a 250 cm tube, as opposed to the 30 cm one that was used, would have been closer to the mark. Then, the amount of carbon dioxide was reduced by a third: they found what they regarded as very little change and came to the conclusion that the absorption bands of the light spectrum at which carbon dioxide absorbs were quickly saturated - clogged-up, so that their absorption would not increase.

Another problem raised at the time was that water vapor also absorbs infra-red radiation, and in the available and by modern standards rather low-resolution spectrographs of the time, the absorption bands of the two gases overlapped one another. It was thought, therefore, that increasing carbon dioxide would be countered by it being unable to absorb infra-red radiation in bands of the spectrum that the much more abundant water vapor was already blocking.

However, the precision of the measurements obtained by Ångström has since been shown to have been poor: his reported decrease of absorption accompanying a 33% decrease in carbon dioxide concentration was 0.4%, when it would in reality be about 1%, enough to make a significant change to planetary temperatures. Not only that, total saturation in the lower atmosphere is not a problem for the Greenhouse Effect: if the upper layers of the atmosphere remain unsaturated, they will still prevent heat getting out into space. The atmosphere cannot simply be treated as a tube full of gas: it has multiple layers, each with its own properties, and how these layers interact is important.

But back then, it was concluded that Arrhenius was wrong and Ångström moved onto other research, despite Arrhenius publishing a paper critical of the experiments and explaining how in the dry upper atmospheric layers, the role of water vapour was of limited importance. This was - and still is - because water vapor in the upper troposphere occurs in concentrations several orders of magnitude less than in the lower troposphere where most of our weather occurs. As luck would have it, however, nobody took a lot of notice of that and, in effect, the carbon dioxide greenhouse effect hypothesis went to sleep for over two decades. In Part Two, we shall see what happened after the thread was picked up again, in 1931.

Further Reading

Spencer Weart's The Discovery of Global Warming gives a very detailed account of the history of climate science with a plethora of references - there are many days' worth of in-depth study there for those who want to go beyond the blogosphere!

Comments

RE: "Not only that, total saturation in the lower atmosphere is not a problem for the Greenhouse Effect: if the upper layers of the atmosphere remain unsaturated, they will still prevent heat getting out into space."

I understand what this means, and it is not wrong, but I think it could be misinterpreted to mean that unsaturated levels of CO2 still prevent _all_ heat from getting to space. The effect is more of a restriction of outflow than a prevention.

Absorbance is a function of density, and density drops with altitude. Raising the concentration of CO2 in the atmosphere raises the density (partial density to be pedantic) throughout the column, and that effective raises the altitude of whatever you might consider the cutoff between saturated and unsaturated. A thicker blanket reduces heat loss more than a thinner one.

It strikes me as supreme hubris when I come across those who doubt that more CO2 will lead to more energy retention; it's as though they think they know something that 200 years of hashing out the details of how this works has not already discovered. It's not impossible, but you'd better bring the goods, and no one I've ever come across has.

Sometimes, while thinking of the importance of infra-red in this whole business, I like to start with Herschel in 1800. His realization provided a backdrop to all subsequent thinking on climate science even though he was not thinking about climate.

Excellent article in the new issue of American Scientist about William Herschel's experiments with infra-red. He quickly realized (in 1800) that he'd have to isolate his thermometers from the effects of conduction and convection in order to study radiation. That's a lesson that many more modern would-be Galileos haven't figured out!

The time-line graphic is a good answer to those who who have been misled into thinking that AGW theory is all about computerised climate models.

The article in American Scientist that muoncounter links @ 6 is behind a paywall, unfortunately, but the abstract is tantalising. The degree of sophistication in scientific experiments two hundred years ago still has the capacity to surprise me. What the early investigators discovered, using primitive equipment by today's standard, is remarkable.

Indeed, Doug. It also serves as a very effective answer to people who are apt to post comments that infer that climate science only started out about 20 years ago or that there would be no climate science if Mike Mann (no disrespect intended) didn't exist!

To whom it may concern, here's Herschel's paper. Let me quote from his conclusions:

"To conclude, if we call light, those rays which illuminate objects, and radiant heat, those which heat bodies, it may be inquired, whether light be essentially different from radiant heat? In answer to which I would suggest, that we are not allowed, by the rules of philosophizing, to admit two different causes to explain certain effects, if they may be accounted for by one."

Given that at his times they didn't know what light and heat are, it's a remarkable intuition.

The problem with Arrhenius's upper atmospheric response is that stratospheric temperatures are primarily a direct response to the solar constant and it's variation over the course of the year.

The amount of energy that reaches the stratosphere from the troposphere is limited. This leaves the Earth's distance from the Sun as the primary driver of the stratospheric temperature variation.

The coldest stratospheric temperature also took place in mid-2008 when the Sun was unusually quiet and the Earth was the maximum distance from the Sun. Since the Sun has become more active, stratospheric temperatures have increased.

If the upper atmosphere's temperature isn't impacted by the CO2 absorption, it would appear as if Ångström was in fact correct, even if his measurement was not perfect by today's standards.

The Inconvenient Skeptic - "The problem with Arrhenius's upper atmospheric response is that stratospheric temperatures are..."

Are you aware that Arrhenius published "On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground" in 1895, while the stratosphere itself was not discovered until five years later? With detailed knowledge of stratospheric structure and response coming after that?

Arrhenius can hardly be blamed for not detailing changes (such as stratospheric cooling with increased GHG concentration) before anyone knew about the stratosphere.

Add to that what muoncounter pointed out - that your objection regarding insolation and stratospheric temperatures has no basis in fact - and your post objecting to Arrhenius is quite, um, curious...

As usual the readers on this site focus only on anomaly which is why they consistently miss the point.

The stratospheric temperature that I show is the average daily temperature for the past 9 years. Temperature (not anomaly) changes over the course of the year. What causes the actual temperature to change is what I am discussing.

The stratospheric temperature is directly dependent on the amount of energy the Earth is getting from the Sun. Over the course of the year the Earth's distance from the Sun changes. That is the dominant factor in determining the amount of energy the Earth is getting.

The Earth is farthest from the Sun in July and closest in January. The means in January the Earth gets the most energy and in July the Sun gets the least energy. The stratospheric temperature reflects that same behavior while the Earth's surface does not.

Arrhenius stated that in the upper atmosphere (i.e. above the level where water vapor exists) that an increase in CO2 would not be impacted by that water vapor. I am simply pointing out that the stratosphere shows no dependence on the Earth's surface. This would indicate that the amount of CO2 can have no impact on the upper atmosphere.

Ignoring the facts in this case is pointless because there isn't a debate on this. I am simply pointing out that the article states the response to Arrhenius, but fails to mention that the temperature of the stratosphere is independent of the surface and the troposphere. Of course Arrhenius didn't know that when he said it, but the author should have known that.

"As usual the readers on this site focus only on anomaly which is why they consistently miss the point."

The readers of this forum focus on the peer-reviewed literature published in reputable journals. They also focus on debunking the memes promulgated by fake-skeptics...

"The stratospheric temperature that I show is the average daily temperature for the past 9 years."

And thus utterly lacking in any significance, statistically.

"The stratospheric temperature is directly dependent on the amount of energy the Earth is getting from the Sun."

You conveniently omit it is also directly dependent upon the amount of GHG's present in the atmosphere. And upon the levels of CO2...directly.

"The means in January the Earth gets the most energy and in July the Sun gets the least energy. "

You may want to revisit this assumption. Unless you are implying the Sun receives back radiation from the Earth...

"This would indicate that the amount of CO2 can have no impact on the upper atmosphere."

Utter Horse-hockey. That the stratosphere's temperatures can be affected by levels of CO2 is foundational to GHG functionality. Another point utterly without debate by those who understand the science.

"Ignoring the facts in this case is pointless because there isn't a debate on this. "

Correct. That you are wrong is a fact, without debate. And that the facts are inconvenient to the agenda you consistently prosecute is also not contested. As usual.

You are correct that I mis-typed that the Sun (meant Earth) receives the least energy in July. Thanks for noticing that.

Jumping to the point then. If it isn't the solar energy that is causing the phasing of the stratospheric temperatures, then what is?

I welcome an explanation of how GHG's manage to cool the stratosphere while the Earth is warmest and vice versa. Unless of course you are discounting all the work of Phil Jones that shows the Earth's maximum temperature is ~16C in July while it is ~12C in January.

I would like to point out that it is not expected that GHG warming, which works in decadal timescales, should be clearly evident in seasonal cycle of stratospheric temperature. Everybody knows that Earth's seasons are due to Earth's orbital parameter changes, but it has nothing to do with GHG warming.

So Daniel still has not answered the question of why the stratosphere's temperature cycle is de-coupled from the troposphere on the seasonal scale which is the point that I have been making the entire time.

Arrhenius was right (and lucky) because the emission layer is inside the troposphere. In fact, Arrhenius' results have been confirmed by Hulburt some decades later by taking into account the temperature structure of the troposphere-stratosphere and the effect of water vapour, CO2 and Ozone.
On passing, even a cursory analysis of the temperature structure should tell why the stratospheric temperature follows the insolation annual cycle.

Nor have you answered the questions regarding your assertion and use of unsuitable data in #10. Add to that the questions raised subsequently: What does annual 'phasing' of stratospheric temperature have to do with the subject at hand? What does the regular change in the earth-sun distance have to do with the subject at hand?

"So Daniel still has not answered the question of why the stratosphere's temperature cycle is de-coupled from the troposphere on the seasonal scale which is the point that I have been making the entire time."

Your "point" is specious (a straw-man argument) and off-topic. Please constrain your comments to the topic of the OP or I'm sure the moderators will constrain them for you.

It is noted that you meticulously avoid answering the questions most inconvenient to your cause.

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Moderator Response: TC: Point well taken. This discussion is of topic, and should be taken to a more suitable thread.

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